Primer coating composition

ABSTRACT

A primer coating composition, particularly for use with polyvinylidene fluoride topcoating comprising an aqueous acid coating composition having phosphate ions and ions of the group of chromate ions or molybdate ions, and particulate of polyvinylidene fluoride.

The invention relates to a primer coating composition comprisingpolyvinylidene fluoride and a phosphate composition, and with articlesof manufacture so coated to obtain improved adhesion between thesubstrate and a polyvinylidene fluoride topcoat. The invention furtherrelates to laminates formed on a substrate with a polyvinylidenefluoride topcoat composition.

There is widespread demand in industry for protective coatings whichwill withstand the effects of severe environmental conditions. Manyprotective coatings are currently available but have limited solventresistance and/or weathering characteristics, i.e. polyesters, acrylics,epoxies. Polyvinylidene fluoride has a unique combination of physicaland chemical characteristics which has led to its use in a variety ofcoating applications. Physically, this polymer, which is flexible at lowtemperatures, possesses high thermal stability. Chemically, this polymeroffers excellent resistance to salt spray, humidity, solvents andstains. As compared with conventional coating polymers, polyvinylidenefluoride has exhibited better color longevity and weathering propertieson exterior exposure. However, polyvinylidene fluoride has exhibitedlimited bonding properties with conventional primers.

One of the problem areas in the use of polyvinylidene fluoride is in thefield of coil coating. The coil coating process is a high volume meansof applying a wide variety of coatings to a moving strip of metal. Thismetal can be aluminum, cold or hot rolled steel, hot dip or electrogalvanized steel or a limited variety of zinc-aluminum clad steels.

The metal is usually supplied to a coating applicator in the form of aflat "sheet" wrapped upon itself. This "sheet" can vary in length andwidth, typically 18 inches to 60 inches or 72 inches wide by severalthousand feet in length and can weigh upwards of several thousandpounds. Conventional polyvinylidene fluoride type coil coatings arefactory applied and oven fused to the properly prepared substrate. Thesepremium finishes are typically applied to architectural buildingcomponents such as metal siding, louvers, fascias, window walls, metalroofing, etc. These components are commonly post formed from theprecoated coil stock. Therefore, these finishes must exhibit excellentproperties of appearance and color durability, abrasion resistance andflexibility.

In order to achieve the aforementioned performance characteristics, aseries of processing steps must be performed on the coil after it isreceived from the metal supplier.

Coiled metal is threaded into a coil coater and drawn at a high rate ofspeed through various stages of pretreatment, priming, and topcoatingand baking until it emerges from the other end of the coil coater and itis rewound as precoated coil. This method of coating permits criticalcontrol of quality at every step in the operation. Automatic monitorequipment maintains constant conditions in cleaning and chemical bathsto assure an optimum surface for applying the coating. The applicatorrolls that apply the coating are accurate enough that dry filmthicknesses (DFT) as low as 1/10 mil (0.0001 inches) can be deposited onthe flat surface of the moving strip.

Along with providing superior quality, coil coating is highly versatile.In a single pass through the coil coating unit, a strip of metal mayreceive various combinations of primers and finish coats on both sides.The coating may subsequently be embossed or custom printed, creatingsuch decorative or functional effects as wood grain patterns, trademarksor textures. A strippable film may be applied to protect the finish, ora coating of wax or other lubricant rolled on to assist in fabrication.Line speeds may be as high as 600 feet a minute but typically run on theorder of 300-400 feet per minute.

In the coil coating operation, the coil is mounted on an unwinderspindle. From the unwinder spindle the strip is looped through anaccumulator tower. This tower is used to provide storage of the metalstrip so that the strip joiner (a device that stitches the end of onecoil with the beginning of another) can operate while the line in frontof the tower continues to run. After this initial "feeding" stage theactual pretreatment and coating of the metal is performed.

A pretreatment section of the coil coater simultaneously cleans bothsides of the metal strip with chemical sprays and rotary brushings. Inaddition, a chemical conversion coating (e.g. phosphating) is applied toform a surface to promote adhesion of the primer coat. Afterpretreatment, the strip exits this section totally clean, dry and readyfor primer application.

The clean metal strip then enters the first of two painting steps. Herethe primer coat is applied to one or both sides of the strip. After theprimer coats are applied, the strip is fed directly into the primer ovenwhich quickly heats the metal and primer to the required curingtemperature. Upon exiting from the primer oven, the metal strip entersthe initial quench where it is cooled by a combination of air and waterand then thoroughly dried. At this point the primer has become anintegral bonded film ready to accept the finished coat. The surface ofthe strip that will be exposed to the elements will receive the topcoatwhile the bottom of the strip may receive a "backing" coat (i.e. anaverage performance finish more receptive to adhesives used with rigidfoam insulation or some other type of material which would later providerigidity to the fabricated building panel). The topcoat oven is similarto the oven used to cure the primer. It also quickly heats and cures thecoated metal strip. The second and final quench cools the precoated coilto near room temperature so as to complete the basic coil coatingoperation.

The precoated strip then enters the exit accumulator tower, which willbegin to accumulate the metal only when it becomes necessary to remove acoil from the recoiler. This action allows the coil coater to maintainits continuous operation.

Curing of these coatings is achieved by passing the strip through anoven zone with temperatures in the range of 700°-900° F. Since the stripis moving at a fast rate of speed, it does not reach these temperaturesbut achieves what is known as peak metal temperature (PMT). This PMT isdesignated by the coating manufacturer as that temperature needed tocure the coating. These are typically in the range of 450°-480° F. forthe polyvinylidene fluoride systems and can be achieved by a balance ofline speed and oven zone temperature.

To the dried primer coating is applied the final coating which is acommercial polyvinylidene fluoride based topcoat such as Fluropon®(DeSoto, Inc.), Duranar® (PPG Industries) or Nubelar® (Glidden Coatingsand Resins). The polyvinylidene fluoride topcoats, when applied by coilcoating techniques, have dry film thicknesses of 0.7-1.3 mils.

Following the coil coating operation, the precoated coil is fabricatedand thus the cured coating laminate is subjected to a number of physicalstresses which include stretch, compression, shear, shock andinterruption. The result is that the coating may tend to crack or crazeand there is a loss of adhesion in areas which can affect the aestheticproperties. Loss of adhesion or weak adhesion between the polyvinylidenefluoride topcoat and the substrate, particularly where a severeenvironment is encountered, results in a loss of physical properties andchemical resistance. Also, the application of polyvinylidene fluoridetopcoatings on all substrates by spray methods utilizing conventionalprimer coatings has not been successful in producing a desirableproduct. For example, the brochure of DeSoto Inc., 1700 S. Mt. ProspectRd., Des Plaines, Ill., entitled "FLUROPON® Architectural Coating"states that FLUROPON, a coating composition comprising polyvinylidenefluoride, is only approved in spray coating for use on aluminum.Surprisingly, the primer of the invention permits spray coatingapplication on other metallic substrates and by other methods than spraycoating.

Polyvinylidene fluoride topcoats as supplied by manufacturers are basedon rather strict formulation guidelines as dictated by the resinmanufacturer (Pennwalt Corp., King of Prussia, Pa.). They areessentially blends of polyvinylidene fluoride resin (Kynar 500) withacrylic modifiers. They also contain pigments to produce the colorrequirements; and while most of these pigments do block UV, use of thosethat do not can lead to inconsistent performance on exposure to theelements and thus severely limits the color ranges available. Thesetopcoats also contain blends of solvents, usually aromatic and highboiling ketones, to aid in flow and leveling and film formation. Theymay also contain waxes which aid the film in the fabrication steps. Themanufacturers may also include proprietary "tracers" to enable coatingidentification once the building panels are in place. It is known to usesuch topcoats with the epoxy primers. However, the epoxy primers aresubject to deterioration from UV which affects the topcoat physicalproperties and chemical resistance. The primer of the invention, becauseit is formulated with a large portion of inorganic materials, is notaffected by UV radiation to the same degree as the epoxy primers.

One of the applications of the primer of the present invention is inconnection with coil coating processes as previously described. Theconventional primers currently used in coil coating processes withpolyvinylidene fluoride systems are epoxy based coatings containinginhibitive pigments; for example, zinc and/or strontium chromates. Theepoxies form good adhesive bonds to the substrate but are susceptible todegradation when exposed to long term UV radiation. This degradationeventually leads to intercoat adhesion loss and substrate adhesion loss.This then makes the entire system more prone to corrosive attack andthus leads to deterioration of the substrate. The susceptibility of theprimer to UV comes about because of the inability of the polyvinylidenefluoride resin in the topcoat to block UV radiation even in pigmentedsystems.

The above illustrates the topcoating compositions which are commerciallyavailable and the generic primer compositions which are commonlyutilized that provide those disadvantages over which the presentinvention is intended to overcome. The primer coating of the inventionovercomes these disadvantages and provides additional advantages as willhereinafter be made obvious through the combination of phosphate ionsand ions of the group of chromate and molybdate ions, and particulate ofpolyvinylidene fluoride. Among some of the advantages of the primercoating composition of the invention is its ability to withstanddeterioration when subjected to UV, capability of application to a widevariety of different metallic substrates by different methods, improvedphysical properties and chemical resistance.

It is known that phosphate and chromate/phosphate coatings are useful toprotect metal surfaces. For instance, Kirk and Othmer, Eds.,Encyclopedia of Chemical Technology, 2nd ed. vol. 18, IntersciencePublishers, a division of John Wiley & Sons, Inc., 1969 (pages 292-303),describes phosphate and chromate coatings. The United States patentliterature describes coating solutions or dispersions for protectivecoating of metals, which compositions are suitable for use as componentsof the compositions of the invention. Such suitable compositions aredisclosed by Allen (U.S. Pat. No. 3,248,251); Brumbaugh (U.S. Pat. No.3,869,293); Collins (U.S. Pat. No. 3,248,249); Wydra (U.S. Pat. No.3,857,717); Boies (U.S. Pat. No. 3,081,146); Romig (U.S. Pat. No.2,245,609); Helwig (U.S. Pat. No. 3,967,984); Bennetch (U.S. Pat. No.3,443,977); Hirst (U.S. Pat. No. 3,562,011) and others. Thesedisclosures are incorporated herein by reference. Other illustrativepatents or literature showing corrosion inhibiting and protectivecoating compositions of phosphates, mixtures of phosphates and chromatesand/or molybdates are known to one skilled in the art and furtherexamples need not be supplied. These compositions can be utilized in thepresent invention with or without the additives disclosed herein.

According to the present invention, there is provided a primer coatingcomposition which causes a more effective adhesion of a polyvinylidenefluoride topcoating to different varieties of substrates and which canbe applied by any of the methods of spraying, dipping, brushing, etc.The primer coating composition comprises (a) an aqueous acid coatingsolution comprising phosphate ions and ions of the group of chromateions and/or molybdate ion, and (b) about 3 to about 60% by weight ofparticulates of polyvinylidene fluoride, preferably, 10 to 20% by weightof polyvinylidene fluoride. When the amount of polyvinylidene fluorideis below this range the beneficial effect of the presence is hardlynoticed. Utilizing a larger amount is costly and causes difficulty inuniformly applying the composition.

Typically, the combination of compounds in said above-mentionedphosphate solution (a) is such as will provide at least 0.1 mole perliter of dissolved phosphate (preferably 0.5 mole per liter), and atleast 0.2 mole per liter of a compound from the group consisting ofchromate and molybdate.

In the phosphate solution it is not necessary that a metal ion be added.When the phosphate and/or chromate or molybdate ion is furnished to thesolution by addition of a metal salt, as is often done, metal ion isinherently supplied to the solution. Hence, any of the known phosphates,chromates, dichromates or molybdates can be used as the source of metalion. Additionally, as is known, metal ion can be supplied in a form suchas metal oxide, hydroxide, carbonate, etc. which will dissolve in acid,i.e. phosphoric acid, chromic acid or molybdic acid, to produce themetal phosphate, chromate or molybdate, and therefore the metal ion pluswater and/or gas which is evolved. The following metal compounds willillustrate those which can be added to generate the metal ion within thesolution, by an acid-base reaction, in accordance with the above:magnesium oxide; magnesium hydroxide; zinc oxide; zinc hydroxide;aluminum hydroxide; lithium oxide; lithium carbonate; and calciumhydroxide. Metal compounds which may be added to generate the metal ionin solution are various oxides, hydroxides or carbonates of magnesium,zinc, aluminum or others. Such procedures and sources for the metal ionsare known and reference may be made to the cited '251 Allen patent, forinstance, column 7, lines 26-57, which is incorporated herein byreference.

In the preparation of the primer coating composition, the polyvinylidenefluoride particulate can be added directly into the phosphate solutionand with rapid stirring obtain a uniform mixture. However, when a coilcoating composition is being prepared it is preferable that thepolyvinylidene fluoride particles are first formed into an aqueousuniform dispersion by stirring so as to obtain a smooth product prior tocombining with the phosphate solution. A nonionic surfactant togetherwith a defoamer is advantageously utilized to wet the resin in formingthe dispersion.

The polyvinylidene fluoride particles in the dispersion are present inan amount of about 15 to about 30% by weight of the dispersion,preferably about 20 to about 25% by weight.

For most applications, the polyvinylidene fluoride ideally has aparticle size of less than 325 mesh. However, submicron particle sizeand particles of less than 100 mesh have been used for certainapplications. As the particle size gets larger, the smoothness of thecoating is affected.

In accordance with the invention, coated articles are provided whichcomprise a substrate, a primer coating fused thereon and a topcoat of apolyvinylidene fluoride composition. A polyvinylidene fluoride topcoatwhich has been found to be suitable for use over the primer compositionof the invention is commercially available under the trademark FLUROPONproduced by DeSoto Inc., 1700 S. Mt. Prospect Rd., Des Moines, Ill.Likewise, the Nubelar® and Duranar® topcoats would also be suitable.These topcoats are solvent dispersions of polyvinylidene fluoride powderand a thermoplastic acrylic polymer. They are also known to contain aplasticizer, pigmentation and waxes for slip and abrasion resistance.The polyvinylidene fluoride particles in the commercial topcoat commonlycomprises about 50 to about 95% by weight of the topcoat based on thetotal solids.

It has been found to be advantageous but not necessary to utilizecertain additives in the primer coating compositions of the invention.Among the additives which may be added are fumed silica, colloidalsilica, fumed alumina, colloidal alumina, aluminum powders, nonionicsurfactants, defoamers, etc. Fumed silica can be added to the phosphatecomposition as a rheology modifier together with, before or after thepolyvinylidene fluoride, without any significant change in the endresult. The amount of the fumed silica or other additives which may beadded to the chromate/phosphate composition need generally not be morethan about 10%, preferably from about 0.25 to about 5% of the totalsolids in the coating composition.

Typical fumed silica such as Cab-O-Sil M5 used in accordance with theinvention generally has the following characteristics:

    ______________________________________                                        silica content (dry basis) %                                                                      99.7-99.99                                                particle size, μm                                                                             0.007-0.05                                                 surface area, m.sup.2 /g                                                                          50-400                                                    bulk density, lb/ft.sup.3                                                                        2.3-7                                                      loss of ignition (1000 ° C.),                                                             0.5-2.5                                                    moisture free basis                                                           ______________________________________                                    

Generally, the fumed silica which is prepared from silicon tetrachlorideby high temperature hydrolysis is about 98.8% SiO₂. It consists ofclusters of particles, 10-40 μm in size with a surface area of 250 to300 m^(2/) g and a refractive index of about 1.4. The particles have anegative charge. The surface area of the products, the outside surfaceof the spheres and the surface itself consists of both silanol groupsand siloxane groups, to have been determined to be 1 silanol group forevery 30sq. A⁰ of surface. A preferred fumed silica (or silicon dioxide)is that available commercially under the name of Cab-O-Sil. Cab-O-Sil isdescribed to be constituted of silica spheres averaging 7 to about 14millimicrons. The final surface areas may range from 400 square metersper gram through 200 square meters per gram, respectively.

The coating compositions of the invention advantageously include awater-soluble, acid-stable nonionic surfactant which is capable of anddoes form a three dimensional, cross network with the silica which maybe present in the composition. The surfactant wets the polyvinylidenefluoride so as to provide a smooth uniform mixture of the resin in adispersion and acts as a stabilizer for the primer coating compositions.Preferably, the surfactant is an ethoxylated alkylphenol oralkylphenoxypoly (ethyleneoxy) ethanol, an ethoxylated aliphaticalcohol; polyoxyethylene, a carboxylic ester like a glycerol ester (monoor di -), a carboxylic amide like a polyoxyethylene fatty acid amide andother equivalent nonionic surfactants. Typical suitable ethoxylatedalkyl phenol are alkylphenols of C₈ -C₁₂ alkylphenols. If it ispreferred that they be water-soluble, those having at least 60 weightpercent of polyoxyethylene groups are particularly well suited. Suchethoxylated alkylphenols are well-known under various trademarks such asIgepal, Levelene, Neutronyx, Solar NP, the Surfonic series, and theTriton N and X series, just to name a few.

Amongst the polyoxyethylenes suitable for use in accordance with theinvention are the mono and dialkyl ethers of ethylene glycols and theirderivatives. If it is preferred that they be water-soluble, those havingat least 60 weight percent of polyoxyethylene groups are particularlywell suited. Typical of such nonionics are the ethylene glycol monobutylether, ethylene glycol monobutyl ether acetate, ethylene glycolmonoethyl ether acetate, ethylene glycol dibutyl ether, ethylene glycolmonohexyl ether, ethylene glycol monomethyl ether, ethylene glycolmonomethyl ether acetate, ethylene glycol monophenyl ether and otherequivalent ethers or ethylene glycol. Another group of nonionicsparticularly well suited for the preparation of the coating compositionsof the invention are the polyethylene glycol and the alkoxy,particularly lower alkoxy, such as methoxy polyethylene glycol; alsodiethylene glycols, propylene glycol and other similar glycols.

Suitable nonionic surfactants for use in the invention are disclosed inKirk & Othmer, Encyclopedia of Chemical Technology, ed. vol. 19, pages531 to 554 entitled "Nonionic Surfactants," which is incorporated hereinby reference. The nonionics used herein are stable and inert to theacidic conditions prevailing in the phosphate solution and thecompositions of the invention.

It is an aspect of the invention that the nonionic surfactant be capableof and does form a three dimensional cross-linked network with the fumedsilica so as to provide suspension to the finely dispersedpolyvinylidene fluoride resin particles.

The nonionic surfactant therefore contributes favorably to theproperties of the composition. Accordingly, it is preferred that thecoating compositions contain from about 0.01 to about 5% by weight andmore preferably about 0.02 to 0.6% by weight of the surfactant based ontotal solids.

The sequence of admixing the fumed silica and the nonionic surfactantwith the phosphate coating solution is not critical. Either one of thesetwo components may be first admixed to the phosphate solution to form anintermediate liquid composition, and then the second component may beadmixed to form the final primer coating composition.

If it is desired to prepare coating compositions which are especiallywell-suited for dip/spin, or application by dipping, the compositionwould contain these certain amorphous fumed silicas and a nonionicsurfactant in amounts which would cause the composition to bethixotropic. Such suitable additives (and the resulting compositions)are described in copending application Ser. No. 06/441,754, filed Nov.15, 1982, now abandoned which is incorporated herein by reference.Likewise, the compositions of the invention may be made thixotropic byincorporation of certain aluminas as disclosed in copending applicationSer. No. 05/485,748, filed Apr. 18, 1983, which is incorporated hereinby reference.

In accordance with the invention, a particular primer coatingcomposition has been found which is stable, i.e. it does not undergodegradation and does not classify or separate into its components, uponlong storage periods (shelf stability) under conditions of use. Also, itcan be applied on substrates other than aluminum by the spray method.

It is noteworthy that in accordance with the invention, a greaterlatitude is provided in the type of phosphate compositions which can beused. For instance, with respect to the Allen Pat. No. 3,248,251, it isnot necessary that the phosphate solution be limited to the variousconcentrations and other molar relationships disclosed by that patent.The present invention, therefore, allows for the use of a large numberof and a great variety of acidic phosphate solutions for making theprimer coating compositions.

It is understood that the amount of polyvinylidene fluoride resinutilized in the primer coating composition depends on the amount ofsolids in the binder composition, the end use of the coating, the typeof substrate and the method of applying the coating on the substrate.

It is preferred to maintain the chromate/phosphate ratio constant so asto improve formability. It is also preferable to have the metal ionconcentrations low to improve curing at lower temperatures. In thecomposition the preferred metal ion is magnesium; however, zinc andaluminum ions can also be utilized.

The primer coating compositions of the invention are highly desirablefor use in a coil coating process as well as for other methods ofapplication and substrates.

The ingredient ranges for primer coating compositions, resin dispersion,and phosphate solutions utilized in their preparation are as follows:

                  TABLE I                                                         ______________________________________                                                    Resin   Phosphate                                                             Dispersion                                                                            Solution  Coatings                                        Ingredients (g/l)                                                                           low    high   low  high low  high                               ______________________________________                                        Mg as MgO                    0    40  0    20                                 Cr.sup.+6 CrO.sub.3         14   228  7    114                                PO.sub.4.sup.-3 as H.sub.3 PO.sub.4 (85%)                                                                 37   564  12.5 282                                SiO.sub.2                    0    88  0    44                                 Defoamer       0     90               0    45                                 Surfactant    0.1    25               0.1  25                                 Polyvinylidene                                                                              30     600              30   600                                Fluoride                                                                      pH            3.0    6.0    0.01 1.5  0.4  2.0                                ______________________________________                                    

The pH of the coating compositions of the invention are preferablybetween 0 and 3, more preferably 0-2. At these pH ranges, rapid curingis promoted.

Before starting the treatment with the primer compositions of thepresent invention it is, in most cases, advisable to remove foreignmatter from the metal surface to be coated by thoroughly cleaning.Cleaning may be accomplished with known agents; for instance, withagents containing sodium metasilicate, caustic soda, carbontetrachloride, trichloroethylene, and the like, depending on thesubstrate to be coated. Commercial alkaline cleaning compositions whichcombine washing and mild abrasive treatments can be employed forcleaning, e.g. an aqueous trisodium phosphate-sodium hydroxide cleaningsolution. In addition to cleaning, the substrate may undergo cleaningplus etching.

After the primer coating composition has been prepared and thoroughlymixed, it can be applied to a surface by using a spray, dip, knife, flowor roller coating technique depending upon the viscosity of thedispersion, solution or slurry. After the primer composition has beenapplied to a substrate by any of the above techniques, it is fused intoa continuous adherent film by heating. Fusion temperatures range betweenabout 350° F. and about 500° F., preferably between about 450° F. andabout 560° F., typically 500° F. to 520° F.; and are applied for aperiod of from about a few seconds to about 2 hours, preferably for aperiod not in excess of about 1 hour. Generally, the higher the fusiontemperature the shorter the residence period of the primer coatingcomposition at that temperature. The residence period is also determinedby the method employed for heating. For example, the substrate may beplaced in an oven and baked for a period of hours or it may be heated ata very high temperature (about 700°-900° F.) for a few seconds unitl itreaches a peak metal temperature.

Subsequent applications of primer coat may be laid down in the mannerstated above, allowing each layer to dry and fusing after eachapplication. When the primer coating composition is to be used as afinal coating, layers of the primer coating composition can be laid downup to thicknesses about 10 mils or higher, although coatings of morethan 1 mil generally are not required.

The following examples illustrate the preparation of the coatings of theinvention and are not to be considered limitations thereof.

EXAMPLE 1

A coating composition for freshly passivated hot-dipped galvanized coil(Parker Bonderite 1303) was prepared as follows:

A. A phosphate solution having the following ingredients was prepared.

    ______________________________________                                        Water (deionized)       800    ml                                             Magnesium oxide         10     g                                              Chromic acid            57     g                                              Phosphoric acid (85%)   100    ml                                             Fumed silica (Cab-O-Sil M-5)                                                                          33     g                                              ______________________________________                                    

The ingredients were mixed and then diluted to 1 liter with deionizedwater.

B. A resin dispersion was prepared as follows.

    ______________________________________                                        Water (deionized)         900    ml                                           Nonionic surfactant (Triton X-100)                                                                      2.5    ml                                           Defoamer (Colloid 677)    1.0    ml                                           Polyvinylidene fluoride (Kynar 301-F)                                                                   150    g                                            ______________________________________                                    

The ingredients were admixed and then diluted to 1 liter with deionizedwater.

The product of Part A and resin dispersion of Part B were combined inequal volume amounts to yield the primer coating composition having a pHof 0.85-0.9 and producing a dried film thickness of 0.2-0.25 mil. Atopcoat of K-500 based resin composition was applied to yield a totalcoated system of 1.4 mils.

The coating, while adaptable to coil application, can be fully utilizedwith any of the application techniques taught by U.S. Pat. No. 3,248,251including spray, dip and flow-coat to a variety of substrates asillustrated by the following additional examples.

EXAMPLE 2

A coil coating primer composition for coil aluminum was prepared asfollows:

A. Preparation of phosphate solution.

    ______________________________________                                        Water (deionized)       600    ml                                             Magnesium oxide         20     g                                              Chromic acid            114    g                                              Phosphoric acid (85%)   200    ml                                             Fumed silica (Aerosil 200)                                                                            33     g                                              ______________________________________                                    

The ingredients were admixed and diluted to 1 liter with deionized waterto form the aqueous phosphate portion of the primer.

In the preparation of the phosphate solution the fumed silica may besubstituted by aluminum powder, colloidal or fumed alumina.

B. Preparation of resin dispersion.

    ______________________________________                                        Water (deionized)         900    ml                                           Polyvinylidene fluoride (Kynar 301-F)                                                                   150    g                                            Nonionic surfactant (Igepal 630)                                                                        2.5    ml                                           Defoamer (Troykyd 999)    1.0    ml                                           ______________________________________                                    

The ingredients were admixed and diluted with water to 1 liter.

The binder of part A was mixed with the dispersion of part B to producea primer coating composition having a pH of 0.4-0.6. The composition,when applied to a substrate, has a dried film thickness of 0.2-0.25 mil.This primer was topcoated with a K-500 based resin composition to give alaminate system of 1.0-1.2 mils total DFT.

EXAMPLE 3

A primer coating composition for aluminum extrusion was prepared with aresin dispersion of Example 2 and the following composition:

    ______________________________________                                        Water (deionized)       600    ml                                             Magnesium oxide         20     g                                              Chromic acid            114    g                                              Phosphoric acid (85%)   200    ml                                             Fumed silica (Aerosil 380)                                                                            44     g                                              ______________________________________                                    

The ingredients were mixed, diluted to 1 liter with water and thencombined with the resin dispersion to yield a primer coating compositionhaving a pH of 0.8-1.0. The composition when applied to a substrateproduces a dried film thickness of 0.4-0.6 mil. This was topcoated byspray application with a topcoat based on Kynar 202 dispersion for a DFTof 3 mils.

A suitable composition can also be obtained by adding 150 g ofpolyvinylidene fluoride directly into the above-mentioned compositionwith stirring.

EXAMPLE 4

A primer coating composition of the present invention was prepared asfollows:

A. Preparation of phosphate solution.

A solution having the following ingredients was prepared:

    ______________________________________                                        Water (deionized)   600    ml                                                 Magnesium oxide     20     g                                                  Chromic acid        114    g                                                  Phosphoric acid (85%)                                                                             200    ml - dilute to                                                         1      liter with water                                   Fumed silica (Cab-O-Sil M-5)                                                                      33.33  g                                                  Magnesium carbonate 75     g                                                  ______________________________________                                    

Magnesium oxide and chromic acid were mixed with the water, and thephosphoric acid was then added. Dilution to 1 liter with water was made.To this mixture was added with stirring the magnesium carbonate and thefumed silica. The resulting mixture had a pH of 0.95-1.0.

B. Preparation of resin dispersion.

A dispersion of polyvinylidene fluoride powder was prepared as follows:

    ______________________________________                                        Polyvinylidene fluoride (Kynar ES)                                                                     45     g                                             Carbitol acetate         34     ml                                            Water (deionized)        240    ml                                            Silicone defoamer (Dapro DF1181)                                                                       10     ml                                            Surfactant (Pluronic L-61)                                                                             6      g                                             Surfactant (Pluronic F-108)                                                                            6      g                                             Non-silicone defoamer (Dapro 944)                                                                      30     ml                                            ______________________________________                                    

The polyvinylidene fluoride powder was premixed with the carbitolacetate and the mixture was added to a combination of the water,surfactants and defoaming agents. The entire mixture was then ballmilled for four hours. The resulting mixture had a pH of 5.45.

The resin dispersion was then added to the solution of part A in a 2:1volume ratio to give a primer coating composition with a pH of 1.68. Theprimer was applied to aluminum castings and topcoated with Kynar 202dispersion to total film build of 4 mils.

EXAMPLE 5

Following the procedure of Example 1, but modifying the solution of PartA, produced another coating composition suitable for use on a hot-dippedgalvanized substrate (Heatbath Galv-Brite 1121) as follows:

    ______________________________________                                        Water (deionized)       800    ml                                             Magnesium oxide         5      g                                              Chromic acid            28.5   g                                              Phosphoric acid         50     ml                                             Fumed silica (Aerosil 300)                                                                            33     g                                              ______________________________________                                    

The mixture was combined and diluted with deionized water to 1 liter.When combined with the resin dispersion the composition has a pH of1.1-1.2 and produces a dried film thickness of 0.4-0.6 mil. The primerwas topcoated by spray application of Kynar 500 based composition to DFTof 2 mils.

EXAMPLE 6

A primer composition for powder metal steel parts was prepared asfollows:

A. Preparation of phosphate solution.

    ______________________________________                                        Water (deionized)       600    ml                                             Zinc carbonate          47     g                                              Chromic acid            57     g                                              Phosphoric acid         100    ml                                             Fumed silica (Cab-O-Sil M-5)                                                                          33     g                                              ______________________________________                                    

The ingredients were admixed and the mixture was diluted to one literwith water.

B. Preparation of resin dispersion.

    ______________________________________                                        Polyvinylidene fluoride (Kynar 520)                                                                    150    g                                             Water (deionized)        900    ml                                            Nonionic surfactant (Triton X-100)                                                                     2.5    ml                                            Defoamer (Colloid 677)   1.0    ml                                            ______________________________________                                    

The ingredients were admixed and diluted to 1 liter with water.

The solution of Part A was mixed with an equal volume of the dispersionof Part B to yield a primer coating composition having a pH of 1.1-1.3,a dried film thickness of 0.4-0.6 mil.

The curing of the coating may be 15 minutes at 560° F.±10° F. to peakmetal temperature of 500° F., then topcoated with Kynar 202 dispersioncomposition.

A suitable primer composition can also be obtained by adding 150 g ofpolyvinylidene fluoride directly into the phosphate solution withoutfirst preparing a dispersion.

EXAMPLE 7

Following the procedure of Example 6, a primer composition for steelparts was prepared as follows:

A. Preparation of phosphate solution.

    ______________________________________                                        Water (deionized)     600    ml                                               Zinc carbonate        47     g                                                Chromic acid          57     g                                                Phosphoric acid       100    ml                                               ______________________________________                                    

The ingredients were admixed and the mixture was diluted to one literwith water.

B. Preparation of resin dispersion.

    ______________________________________                                        Polyvinylidene fluoride (Kynar 301F)                                                                   150    g                                             Water (deionized)        900    ml                                            Nonionic surfactant (Triton X-100)                                                                     2.5    ml                                            Defoamer (Dapro 944)     1.0    ml                                            ______________________________________                                    

The ingredients were admixed and diluted to one liter with water.

The solution of Part A was mixed with an equal volume of the dispersionof Part B to yield a primer coating composition suitable for steelparts, topcoated with Liquinite PVF₂ powder coating to a DFT of 5 mils.

EXAMPLE 8

A primer composition for zinc die cast parts was prepared as follows:

A. Preparation of phosphate solution.

    ______________________________________                                        Water (deionized)       800    ml                                             Magnesium oxide         10     gm                                             Chromic acid            57     gm                                             Phosphoric acid (85%)   100    ml                                             Fumed silica (Cab-O-Sil M-5)                                                                          33     gm                                             ______________________________________                                    

B. Preparation of primer composition.

    ______________________________________                                        Phosphate solution       1000   ml                                            Polyvinylidene fluoride (Kynar 301F)                                                                   300    gm                                            Nonionic surfactant (Triton X-100)                                                                     5      gm                                            ______________________________________                                    

The ingredients in B were admixed to yield a composition with pH of0.85-0.9. This composition was applied to zinc die cast parts to yield acured primer film of 0.4-0.6 mil DFT. Parts were topcoated with K-500based composition to DFT of 2 mils.

EXAMPLE 9

A primer coating composition of the present invention was prepared asfollows:

A. Preparation of phosphate solution.

A solution having the following ingredients was prepared:

    ______________________________________                                        Water (deionized)  600    ml                                                  Magnesium oxide    20     g                                                   Chromic acid       114    g                                                   Phosphoric acid (85%)                                                                            200    ml - dilute to                                                         1      liter with water                                    Fumed silica       33.33  g                                                   Magnesium carbonate                                                                              75     g                                                   ______________________________________                                    

Magnesium oxide and chromic acid were mixed with the water, and thephosphoric acid was then added. Dilution to 1 liter with water was made.To this mixture was added with stirring the magnesium carbonate and thefumed silica. The resulting mixture had a pH of 0.95-1.0.

B. A 10% alumina dispersion was prepared as follows.

    ______________________________________                                        Water (deionized)      447    ml                                              Conc. nitric acid      42     g                                               Dispersible alumina    45     g                                               ______________________________________                                    

The ingredients were admixed with rapid stirring until a smooth mixturewas obtained.

C. Preparation of primer compositions.

1. To 520 g of the product of Part A is added 428 g of the dispersion ofPart B.

2. For each 100 ml of the combined product of Parts A and B is added 60ml of polyvinylidene fluoride latex (Kynar 32), wherein thepolyvinylidene fluoride has an average particle size which is submicron,to obtain a primer composition according to the invention.

EXAMPLE 10

A primer composition suitable for dip/spin application to electroplatedzinc and/or cadmium fasteners and small parts was prepared using thephosphate solution of Example 1. The final composition is:

    ______________________________________                                        A.     Phosphate solution (example 1)                                                                   100 ml                                              B.     Polyvinylidene fluoride latex                                                                    100 ml                                                     (K-32 latex Pennwalt)                                                  ______________________________________                                    

The two items are admixed to give a primer suitable for dip/spin use onplated fasteners and small parts. Parts were topcoated with acomposition based on Kynar 500 resin suitable for exposure to salt sprayand moist SO₂ environments.

COMPARATIVE TEST

The following comparative test was performed on cured laminates whichwere prepared on HDG substrate with the primer composition of Example 1,a commercially available epoxy primer and a sample which contained noprimer. The topcoating consisted of commercial polyvinylidene fluoridetopcoat based on Kynar 500 resin.

    ______________________________________                                        Results                                                                                      Primer of Epoxy                                                Test           Example 1 Primer    No Primer                                  ______________________________________                                        Crosshatch Adhesion                                                                          Pass      Pass      Pass                                       (ASTM D3359 Method B)                                                         Impact (ASTM D2794)                                                           Std            160 in/lbs                                                                              160 in/lbs                                                                              160 in/lbs                                 Reverse        160 in/lbs                                                                              160 in/lbs                                                                              160 in/lbs                                 T-Bend         0-1 T     1 T-2 T   0- 1 T                                     Conical Mandrel                                                                              1/8" pass 1/8" pass 1/8" pass                                  (ASTM D522)                                                                   Salt Spray (ASTM B117)                                                                       750 hrs.  750 hrs.  120 hrs.                                   Scribe         10 clean  4-7 pickoff                                                                             4-6 pickoff                                Field          9         8-10      8 pickoff                                  Edge           10        9         4-5                                        Numerical ratings for salt spray per D1654.                                   ______________________________________                                    

The primer of Example 1 showed the best performance over the epoxyprimer and no primer in the Salt Spray Test. The Scribe Test wasindicative of the damage which would result to the topcoat in an outdoorenvironment. The Field Test is significant as to the integrity of theapplied system. The Edge Test illustrated the condition of sheared edgesof a side of precoated sheet under adverse conditions. The major andmost significant test in the group was the Scribe Test, in which theprimer of the invention showed a definite advantage.

We claim:
 1. A primer coating composition, particularly for use with apolyvinylidene fluoride top coat, which comprises (a) phosphate ions andions of the group of chromate ions or molybdate ions in an aqueous acidsolution, and (b) particulate of polyvinylidene fluoride in (a).
 2. Thecoating composition of claim 1 wherein said polyvinylidene fluoridecomprises about 3 to about 60% by weight of said composition.
 3. Thecoating composition of claim 2 wherein said polyvinylidene fluoride isabout 10 to about 20% by weight of said composition.
 4. The coatingcomposition of claim 1 including a member selected from the groupconsisting of fumed silica, fumed alumina and colloidal alumina.
 5. Thecoating composition of claim 4 including a nonionic surfactant.
 6. Thecoating composition of claim 5 wherein the amount of nonionic surfactantis in the range of about 0.01 to about 5.0% by weight of total solids.7. The coating composition of claim 1 wherein the fumed silica in theamount of 0.25 to 10% by weight of composition.
 8. The coatingcomposition of claim 1 including a defoaming agent and a nonionicsurfactant.
 9. The coating composition of claim 1 wherein the acidcoating solution includes dissolved metal ions of the group ofmagnesium, aluminum or zinc.
 10. A coating which comprises the curedcomposition of any one of claims 2, 4 and
 8. 11. A part coated with thecured composition of any one of claims 1, 2, 4 and
 8. 12. A primercoating composition, particularly for use with a polyvinylidene fluoridetop coat, which comprises (a) phosphate ions and ions of the group ofchromate ions or molybdate ions in an aqueous acid solution, and (b)particulate of polyvinylidene fluoride in (a), said composition having apH of less than
 3. 13. A primer coating composition which comprises anaqueous acidic solution of phosphate ions and chromate ions andparticulate of polyvinylidene fluoride.
 14. The coating composition ofclaim 13 wherein the pH of said composition is not more than
 3. 15. Thecoating composition of claim 13 wherein said polyvinylidene fluoridecomprises about 3 to about 60 percent of said composition.
 16. Thecoating composition of claim 15 including fumed silica in an amount of0.25 to 10% by weight of composition and a non-ionic surfactant wherebya three-dimensional cross-network is formed between said silica and saidsurfactant.
 17. The coating composition of claim 16 wherein the amountof said surfactant is in a range of about 0.01 to about 5.0% by weightof total solids.